Prostate cancer has high incidence in both the United States and Russian Federation. An unresolved problem with a large impact on public health is differential diagnosis of its progressive and metastatic forms. Prostate cancer progression presents a number of fundamental questions that concern the heterogeneity of cell populations within the tumor environment, cell-cell communication, and what defines the invasive phenotype mechanistically. This proposal addresses these issues in an integrative collaboration format within the framework of the U.S.-Russia Bilateral Collaborative Research Partnerships on Cancer. Capitalizing on the complementary expertise of the two collaborating teams, the project aims to improve the differentiation of progressive phenotypes using a recently discovered myosin isoform and to study its mechanistic underpinnings. The unconventional molecular motor myosin IC (isoform A) has been shown to be differentially expressed in samples of progressive prostate cancer. Preliminary results point to its involvement in exosome secretion and an epigenetic transmission of its expression from invasive to noninvasive cells. One aim is to study this process on the electron-microscopic level and its impact on the motility of the recipient cells. We will test the hypothesis of myosin IC involvement in the exosome uptake, which would make its upregulation in the recipient cells adaptive on the cellular level yet contributing to the tissue invasivity via an increased total secretion. This will be tested using shRNA and mutant forms of the isoform. The second aim is to improve differentiation of invasive phenotypes by the isoform A expression. A battery of new samples will be tested and a method developed for cell sorting based on the isoform A expression. If successful, this method will be applied to break down each sample into cell subpopulations in order to increase the differentiation of isoform A-expressing components. The hypothesis is that their relative mass will have a higher correlation with tumor progression, improving the prognostic use of this biomarker. Both aims are fully integrated research plans building on the complementary expertise with the applicant for the linked Russian grant, namely myosin IC molecular biology and biomarker work in the American and electron microscopy and sorting in the Russian laboratory.